The one I have has folic acid and vitamin C also, it's never been a problem. I always give a whole one to adult standard sized birds. If she's half grown then 1/2 a pill should be fine. A whole one would not do any harm, but 1/2 will make them last longer.
I don't know that the wetness would be an issue. If she's low in the pecking order that could contribute if shes' not getting good access to feeders. Sometimes it's hard to know exact causes, vitamin deficiencies are not uncommon and treatment is usually pretty safe, so that is often the first thing to try. At 5 months she could possibly be nearing starting to lay, so that also has to be considered. There are some illnesses that can cause leg weakness, paralysis, and neurological issues, but I would do the vitamins for a while first before jumping to conclusions about anything. Eating and drinking well are good signs, after you feed, I would check her crop and if it's emptying then offer some again. If she's able to eat and drink on her own, I would have it available to her all the time, let her free feed, just give a measured amount so when it's gone or almost gone, you have an idea how much she's eaten. And monitor droppings to make sure they look normal. It would also be a good idea to get a weight on her so you can monitor that, see if she's maintaining or gaining weight, or if she's losing wieght. A digital kitchen scale works well for that. If it's possible to get a picture of her legs, how she stands, it might be helpful. It's also possible that it's a bone deformity. You can look up Varus/Valgus in chickens, there will be images to compare. If it's a deformity or a development/growth issue that has been going on a while, then it may not be correctable.